1. Field of the Invention
The present invention relates to a component mounting apparatus which is used in, for example, automatically successively picking up electric component parts by means of at least one suction nozzle and then mounting electric component parts onto a printed circuit board.
2. Description of the Prior Art
A component mounting apparatus for automatically successively mounting electric component parts onto a printed circuit board has been well known which comprises a plurality of component supply units accommodating respective batches of electric and/or electronic component parts: a movable table on which the component supply units are mounted side-by-side in a row, said movable table being supported for movement in a direction parallel to the row of the component supply units so that at a predetermined supply position an electronic component in a selected one of the component supply units can be taken out from such selected component supply unit: a positioning means for positioning a printed circuit board so that a portion of the printed circuit board onto which the electronic component is desired to be mounted can be aligned with a predetermined mounting position: and a component mounting means capable of retaining the electronic component at the predetermined supply position and then mounting the electronic component onto that portion of the printed circuit board at the predetermined mounting position.
In this component mounting apparatus, the use of a plurality of movable tables is feasible in order that the apparatus can be used for mounting a number of different component parts onto a single printed circuit board, that a loss of time which would occur when the component supply units are replaced with change in type of printed circuit boards may be reduced by reducing the number of changes required, and that a high speed movements can be achieved by reducing a load which would be imposed on the movable table.
In view of the foregoing, the Japanese Laid-open Patent Publication No. 62-140499, published in 1987, discloses a component mounting apparatus which comprises a pair of movable tables supported for movement independent of each other along a common path of movement thereof: a plurality of component supply units mounted on each of the movable tables: a drive unit for each movable table including a screw shaft extending parallel to the common path and a drive motor for driving the associated screw shaft: and internally threaded nuts threadingly mounted on the respective screw shafts and rigidly secured to respective undersurfaces of the movable tables, the movable tables being selectively utilized one at a time depending on conditions under which the component mounting is carried out.
The component mounting apparatus disclosed in the above mentioned publication has been found having some problems. Specifically, the drive unit including the screw shaft and the drive motor is employed for each movable table so that the movable tables can be moved independently of each other. Accordingly, the two screw shafts each having a substantial length corresponding to the stroke of movement of the associated movable table are required, resulting in an increase in manufacturing cost. Also, since each screw shaft for transmitting a driving torque has a substantial length as described previously, the screw shaft tends to undergo a fluctuating motion during the rotation thereof, and therefore, in order to minimize the angle of twist during the drive thereof, each screw shaft must have an increased diameter accompanied by an increase in weight thereof to such an extent as to result in an increase in inertia.
In a system wherein a ball screw is rotated, bearings at opposite ends of the ball screw are loaded to the limit of tolerance enough to result in a displacement in a direction parallel to the path of movement of the table during the drive of each movable table, posing various problems to the facilitation of a high speed component mounting.
The component mounting machine having two component mounting means is also well known. This type of component mounting machine is so designed that the two component mounting means can pick up respective identical components out from a component supply device provided with a single movable table in readiness for mounting on two mounting members which are subsequently moved by a single positioning means to a position above the respective mounting members. While this machine can mount two components simultaneously on a single printed circuit board, the realization of the high speed component mounting and the capability of handing different types of component parts are incompatible with each other.